Acrocanthosaurus

Discovery and Fossil Record

Acrocanthosaurus atokensis was first described in 1950 based on fossils discovered in the early 1940s in Oklahoma, including a holotype and another partial specimen found nearby. Since then, several more specimens have been uncovered - most notably two more complete skeletons in the 1990s - allowing paleontologists to fill in many gaps in its anatomy.

Geographic Range and Environment

This formidable predator lived in what is now the south-central and eastern United States, particularly Texas and Oklahoma, with possible remains found in Maryland. At that time, North America was beginning to split into two landmasses due to the formation of a massive inland sea known as the Western Interior Seaway (WIS), which gradually flooded the center of the continent from the Gulf of Mexico to the Arctic Ocean. This sea eventually created two separate landmasses: Laramidia to the west (modern-day western North America) and Appalachia to the east (including parts of the central and eastern U.S.).

However, when Acrocanthosaurus was alive, the seaway was not yet fully formed, and the areas where it lived - Texas, Oklahoma, and Maryland - were part of Appalachia, the eastern landmass.

The environment it lived in was rich and varied, including floodplains, river deltas, and coastal shorelines, supporting a wide range of plant and animal life. Fossilized footprints from the Glen Rose Formation suggest it also walked along ancient mudflats and beaches. These tracks show several individuals moving in the same direction and has sometimes been suggested as evidence of pack hunting behaviour, though while such behavior is possible this is not strong evidence of that – the footprints may have been left at different times.

There is no confirmed evidence of Acrocanthosaurus in Laramidia, so its known range appears to have been limited to Appalachia, though it may have roamed widely within that landmass. Fossils from Appalachia are much rarer than those from Laramidia because the eastern part of North America had fewer of the sediment-rich environments needed to preserve dinosaur remains. Much of Appalachia was covered in dense vegetation or coastal lowlands, where bones were more likely to decay or be washed away before fossilization. In contrast, Laramidia had active river systems and floodplains that were ideal for quickly burying remains in sediment, leading to far better fossil preservation.

Neural Spines

Size and Weight

Skull and Teeth

Body

Apart from its distinctive spines, the rest of Acrocanthosaurus' skeleton was similar to many of its relatives in the allosauroid group. As a bipedal dinosaur, it had a long and heavy tail to counterbalance its large head and neck so it did not become top-heavy. Its arms were about 1 m long and ended in three sharp, curved claws. Muscle attachment sites on the bones indicate that they were able to pull these arms towards their body strongly – leading paleontologists to believe that they may have played a role in hunting, either by grabbing/restraining prey or by using its sharp claws to slice through flesh.

Movement and Speed

Acrocanthosaurus is not believed to have been a particularly fast runner. In animals — including dinosaurs — the length of the leg bones gives us clues about how they moved. In fast-running dinosaurs, like Ornithomimus or Velociraptor, the lower leg bones (the tibia and the foot bones called metatarsals) are usually longer than the upper leg bone (the femur). This leg structure works a bit like a spring or lever, allowing for longer strides and quicker movement. But in Acrocanthosaurus, the femur (thigh bone) is longer than the tibia and metatarsals. This tells us it was built more for power than speed. A longer femur means stronger muscles and more stability, which are helpful for a big, heavy animal — but it also means it couldn’t move its legs as quickly or efficiently for sprinting. So, this bone arrangement suggests that Acrocanthosaurus was not a fast runner, but likely relied on strength and ambush tactics rather than chasing down prey over long distances. It had a total of 4 toes on each foot, with the first one being smaller and not touching the ground.

Diet and Ecological Role